1. Field of the Invention
This invention is related to a control switch and, more specifically, to a control switch which detects the accumulation of moisture and controls the operation of an associated system based upon the detected accumulation of moisture.
2. Description of Related Art
Referring first to FIG. 1, a typical refrigerator consists of a compressor 10, a condenser 12, a storage tank 14, a throttling valve 16, and evaporator 18 connected by suitable conduits 20 with intake and outlet valves (not shown). The refrigerant stored in the storage tank 14 is a liquid which partly vaporizes and cools as it passes through the throttling valve 16. Among the common refrigerants are ammonia, sulphur dioxide and various halides of methane and ethane. Nearly constant pressures are maintained on either side of the throttling valve 16 by means of the compressor 10. The mixed liquid and vapor entering the evaporator 18 is colder than the near-surround. Thus, the mixed liquid and vapor absorbs heat from the interior of the refrigerator box or cold room and completely vaporizes. The vapor is then forced into the compressor 10, where its temperature and pressure increased as a result of the compression. The compressed vapor then pours into the condenser 12, where it cools down and liquifies as the heat is transferred to outside air, water, or other fluid medium in the condenser cooling coils 12.
In such air refrigeration systems, the evaporator 18 often lowers the air temperature below the dew point. As a result, moisture will condense on the evaporator coil 22. For this reason, air refrigeration systems are also provided with a condensate pan for collecting moisture condensed on the evaporator coil 22. The moisture collected by the condensate pan is then removed by an overflow line. However, dust and other airborne debris may accumulate in the condensate pan and eventually plug the overflow line. In other circumstances, a sewer line to which the overflow line is typically connected may become plugged due to causes unrelated to the air refrigeration system itself. In any event, whenever the condensate pan is prevented from draining, the level of condensate in the pan will steadily increase until the pan overflows, thereby causing water damage to the air refrigeration system.
One solution to this problem was to build a secondary overflow pan connected to a separate overflow line beneath the primary overflow pan. When the overflow line of the primary overflow pan became plugged, condensate would collect in the primary pan until filled. The overflow would then spill over into the secondary overflow pan and drain by way of the overflow line of the secondary overflow pan. While such secondary overflow drainage systems made condensate overflows less likely, they offered no protection from overflows if both drainage systems were blocked. As a result, overflow protection systems often include a switching system to turn the air refrigeration system off in the presence of condensate overflow conditions.
Referring next to FIG. 2, a float activated switching system for an air refrigeration system may now be seen. The air refrigeration system in FIG. 2 consists of a load 24, which may include the air refrigeration system of FIG. 1 connected to a relay via a thermostat of conventional design, connected in series to a low voltage AC source such as a 24 volt AC transformer using electrical connectors 28. The overflow paN 30, which may either be a primary overflow pan or a secondary overflow pan, collects condensating liquid which drains via the overflow line 32. A float actuated switch 34 includes a float 36 positioned in the overflow pan 30 and an electrical contact 38 balanced by a pivot or fulcrum 40. When the level of condensate in overflow pan 30 is low, the contact 38 is engaged with the contacts 28a and 28b of the air refrigeration system 24, thereby permitting power to flow through the load 24, thus maintaining the air refrigeration system 24 in an ON condition. In the event that the overflow line 32 becomes plugged, condensate will begin to accumulate in the overflow pan 30, raising the level of the float 36. When the float 36 has been raised a specified height, the contact 38 will disengage from the contacts 28a and 28b, thereby disconnecting the load 24 from the AC source 26 and turning the air refrigeration system OFF. Unfortunately, due to space limitations during the construction of air refrigeration systems, float actuated switches such as the one described herein are often too large to attach to an overflow pan positioned within the cooling coil housing. In addition, air currents within the cooling coil housing could easily displace the float, thereby resulting in erroneous switching. Finally, float activated switches are particularly undesirable when liquid is draining at a rate just slightly less than the rate at which condensate is being collected by the overflow plan. For example, the overflow line may be partially plugged such that drainage of the accumulated condensate from the overflow pan is occurring at a slightly below normal rate while condensate continues to accumulate at a normal rate. Under these circumstances, the switch could rapidly oscillate between the ON and OFF states, a condition which may result in damage to the air conditioning system.